Lloyd Cluff, director of Risk Management and Director of the Geosciences Department for Pacific Gas and Electric, left, responds to a question while appearing before a Senate select committee looking into California's earthquake preparedness during a hearing at the Capitol in Sacramento, Calif., Monday March 21, 2011. Lawmakers took testimony from various state agencies, natural gas utilities and the operators of California's nuclear power plants on the state's ability to handle an earthquake and possible tsunami like the one the struck Japan last week. Also seen are Steve David, director of site services at PG&E's Diablo Canyon Power Plant, center and Daniel Hirsch, lecturer in nuclear policy at the University of California, Santa Cruz. (AP Photo/Rich Pedroncelli)

Soon after the San Bruno pipeline explosion in 2010, Lloyd Cluff peered into the crater blown in the earth and recalled the risk he had identified there two decades earlier to the company that employed him as a geologist, Pacific Gas and Electric Co.

That was the very spot, Cluff said, that he flagged in a 1990 earthquake-risk analysis as an especially vulnerable point on the gas transmission line that ran from Milpitas to San Francisco, known as Line 132. PG&E already had cited seismic concerns about pipelines in securing $2.2 billion in customers' money from the state to replace them, but it left much of Line 132 in place - including the section that blew up in San Bruno, killing eight people and destroying 38 homes.

"I clearly remember we drew a map, and you will see the place where the explosion occurred," said Cluff, 78, who retired as head of the utility's geosciences division in 2011 after 25 years with PG&E.

"It was circled because we thought there could be a problem," Cluff said. "Our concern was that the pipeline was replaced there and the developer there put in a huge amount of fill. We were worried about the fill settling, posing a risk."

Such warnings about Line 132 from PG&E's own employees - and questions about whether the company actively disregarded them - are likely to be an issue in lawsuits brought by more than 300 plaintiffs against PG&E in civil trials that could begin as soon as this summer.

They are also expected to be a focus of the state's investigation into PG&E's trouble-plagued record-keeping about its gas system leading up to the blast - the detailed findings of which are expected to be released this week.

Unreleased report

Cluff's 1990 analysis is shrouded in secrecy. Although it is mentioned in other documents that have been made public, PG&E refuses to release it and many other seismic-related memos and studies, citing ongoing litigation. But Cluff remembers it clearly.

In an interview last week, Cluff said he had determined that the San Bruno section of pipe sat on fill that was 78 feet deep. The fill could be unstable in an earthquake, he said.

He said he had told PG&E that the section at the bottom of Glenview Drive at Earl Avenue should be a priority for replacement, behind only sections of Line 132 that crossed the San Andreas Fault.

PG&E replaced all the sections that crossed the fault by 1995, but it never got around to the rest of the line, including the part in San Bruno that worried Cluff.

"We gave our report," he said. "The gas system people did what they had to do."

Later downplayed

Two years after Cluff compiled the report, PG&E commissioned another seismic study that downplayed soil instability in the San Bruno area, saying it was not a significant earthquake risk. It identified an area of "low hazard" soil or slope instability just south of Glenview Drive, but made no mention of the eventual blast site itself.

That November 1992 report concluded that most of Line 132 in the San Bruno area did not have to be replaced, because it was "installed using methods that meet current standards."

David Eisenhauer, spokesman for PG&E, said that by 1993, "we evaluated a number of factors and determined that some sections needed to be replaced and some did not."

As for the part of the line where the rupture later occurred, he said: "We determined this section of line did not cross the San Andreas Fault zone and it was already constructed in the street away from potential risk of third-party damage.

"Any further specifics about those decisions are part of ongoing investigations, and we are not able to discuss them at this time," Eisenhauer said.

Lingering questions

Cluff wonders to this day whether the disaster - which was caused in part by the failure of a poorly constructed weld that was coming apart even before the rupture - was set in motion by the settlement of the earth under the line.

He said he had tried to tell his story to investigators with the National Transportation Safety Board, which looked into the reasons for the blast, and to PG&E, but that no one ever got back to him.

"When I looked, I thought, 'My God, we circled exactly where the crater is, where there was the maximum depth of fill,' " Cluff recalled. "I still think that fill had some contribution to the pipeline failure."

The federal safety board's report on the explosion, issued last summer, notes that the 1992 PG&E study found the pipeline segment near the blast was a "low to moderate risk" in a quake. The report made no mention of fill under the 1956-vintage pipe section and did not suggest it contributed to the disaster.

Other warnings

Cluff's warning was not the first time a PG&E employee had voiced concerns about Line 132's seismic safety and recommended replacing long sections of it.

Starting in the early 1980s, the company's gas system design manager, Charles Tateosian, told PG&E officials that notoriously brittle welds could be found on much of the older parts of the 51-mile pipeline.

The welds were made using oxyacetylene technology dating from the early 20th century. The technique generated gas bubbles in the welding bond, making pipes more susceptible to failure during earth movements.

In internal memos, Tateosian identified Line 132 and companion lines 109 and 101 running up the Peninsula as being vulnerable to failure because of the welds and the likelihood of earthquake-related ground shifts. He recommended that the lines be replaced wherever they came within 50 feet of homes.

By 1989, PG&E had replaced portions of Line 101 that were considered to be at risk. Many of the Line 132 welds, however, remain to this day, including in sections that run under homes and businesses.

Like Cluff's report, PG&E has not released Tateosian's memos. They are subject to nondisclosure orders imposed by both the judge presiding over the lawsuits against PG&E and confidentiality provisions of the state utilities code.

But a trail of documents released as part of the San Bruno case shows how the company dealt with Tateosian's concerns.

Systemwide plan

In 1985, three years after Tateosian first sounded the alarm, the company announced a $2.2 billion plan to replace 360 miles of gas transmission pipelines statewide by 2000. After the 1989 Loma Prieta earthquake, PG&E sent Cluff and other geologists out to review the Peninsula pipelines and scheduled replacement work to begin in 1991.

But the work was slow in coming. Cluff recalled hearing about opposition from local cities, including Daly City and San Bruno, which considered it disruptive.

'A lot of decision makers'

PG&E did replace the sections that crossed the San Andreas Fault, including part of Line 132 near the eventual blast site. By 2000, however, PG&E had largely given up on replacing its old lines in favor of monitoring ground movement and inspecting for corrosion.

Cluff said how the company handled his warnings over the years was not something he could control.

"I just advised them on earthquake threats," he said. "A large corporation has a lot of decision makers."

Online: To see Chronicle reports on PG&E pipeline safety since the September 2010 explosion in San Bruno, video of the disaster, and company and government documents about PG&E's actions, go to www.sfgate.com/san-bruno-fire.